Boku ga Boku de Aru Tame ni.

Summary

Second year high school student Shun Asakura has been together with Sana Wakatsuki since they were kids, and has had feelings for her for just as long. In fourth grade, Shun's family had to move, but he couldn't tell Sana how he felt before he left town. He's regretted putting a lid on his feelings for seven years since then, until he finally returns to the town where Sana lives. He resolves to tell Sana how he really feels. But there, he meets Ayumu Fujisaki, who greatly resembles him, and what he thought of himself, like an ideal version of him. (Source: ANN)